The field of the present invention relates to data readers, such as scanners and bar code reading devices. Certain barcode readers are described herein which may be used in both fixed and handheld scanning applications by utilizing distinct optical scan patterns for fixed operation and handheld operation, with each scan pattern optimized for its respective mode of operation, thereby avoiding performance degrading compromises necessary when a single scan pattern is used for both modes of operation.
A barcode label comprises a series of parallel dark bars of varying widths with intervening light spaces, also of varying widths. The information encoded in the barcode is represented by the specific sequence of bar and space widths, the precise nature of this representation depending on which particular barcode symbology is in use. Typical methods for reading barcodes comprise generation of an electronic signal wherein a signal voltage alternates between two preset voltage levels, one representing a dark bar and the other representing a light space. The temporal widths of these alternating pulses of high and low voltage levels correspond to the spatial widths of the bars and spaces. It is this temporal sequence of alternating voltage pulses of varying widths which is presented to an electronic decoding apparatus for decoding.
One common type of bar code readers are spot scanners in which a source of illumination is moved (i.e., scanned) across the barcode while a photodetector monitors the reflected or backscattered light. For example, the photodetector may generate a high voltage when a large amount of light scattered from the barcode impinges on the detector, as from a light space, and likewise may produce a low voltage when a small amount of light scattered from the barcode impinges on the photodetector, as from a dark bar. The illumination source in spot scanners is typically a laser, but may comprise a coherent light source (such as a laser or laser diode) or non-coherent light source (such as light emitting diode). A laser illumination source may offer advantages of higher intensity illumination which may allow barcodes to be read over a larger range of distances from the barcode scanner (large depth of field) and under a wider range of background illumination conditions.
The reading spot of the scanner may be manually moved across the bar code, this type of reader being typically referred to as a wand. Alternately, the spot may be automatically moved or scanned across the bar code in a controlled pattern. A scanning mechanism may comprise a rotating mirror facet wheel, an oscillating mirror, or other suitable means for repetitively moving the illumination beam. The path followed by the scanned illumination beam is referred to as a scan line. Typically, an individual scan line extends across the barcode for the barcode to be successfully read unless specialized piecing software (known as stitching) or electronics are utilized. In addition to the scan engine, a barcode scanner may also employ a set of scan pattern generating optics to produce a multiplicity of scan lines in various directions from the scanner and at varying orientations, thereby allowing barcodes to be read over a large angular field of view and over a wide range of orientations (i.e., a multi-dimensional scan pattern). The scan pattern generating optics typically comprise a set of mirrors aligned at varying angles, each of which intercepts the illumination beam during a portion of its motion and projects it into the region in front of the barcode scanner, hereinafter referred to as the scan volume. Each mirror or mirror set, in conjunction with the scanning mechanism, produces a scan line at a particular position and at a particular orientation.
Another type of data reader is an image reader, such as a CCD reader (charge coupled device), in which an entire line of the bar code image is focused onto a detector array. A CCD reader typically includes a light source to illuminate the bar code to provide the required signal response. For the purposes of this description, the word “scanner” may refer to data readers of both the spot scanner type and the line image type. The following description will focus on barcode reading, but is generally applicable to other types of symbol reading or object identification.
Operationally there are generally two types of scanners, the scanner types being operated in one of two modes, fixed and portable. In the fixed mode of operation, the barcode scanner is fixed while barcoded objects are passed through or held within a relatively large scan volume. In the portable mode of operation, the barcode scanner is moved to the barcode label to be read.
In the fixed mode of operation, a relatively wide angular field of view is required so that a barcode label can be read from the largest possible fraction of the surface of the barcoded object. Since objects are often passed through the scan volume in random orientations, a multi-dimensional pattern is necessary to efficiently read the barcode. In addition, a high scan rate is desirable to allow successful reading of barcodes which are quickly passed through the scan volume.
A simpler scan pattern or a single scan line is often sufficient for portable operation, since the relatively small portable barcode scanner can be rotated to orient the scan line correctly across the barcode. A relatively small angular field of view and a relatively longer depth of field are desirable in this mode of operation. The longer depth of field may also allow the operator to read the barcode from a greater (or closer) distance. The reduced angular field of view reduces the likelihood of inadvertent scanning of other barcode labels, but in turn leads to tighter aiming requirements. To facilitate proper orientation of the scan line relative to the barcode and aiming of the scanner, the scan line may be made sufficiently intense to be seen by the operator. Alternatively, a portable barcode scanner may be provided with pointer illuminators to facilitate aiming of the barcode scanner.
The optimum parameters of operation for a fixed barcode scanner operation are frequently quite different from those of a portable barcode scanner. The particular parameters exhibiting major differences include: number of scan lines, orientation and position of scan lines; angular field of view; depth of field; scan speed; and illumination intensity. However, it may be desirable to produce a barcode scanner capable of both fixed and portable modes of operation. Previously this combined operation has been accomplished by compromising among the various requirements for fixed and portable modes of operation, yielding a barcode scanner which can be used in both modes of operation but with performance inferior to barcode scanners designed for one mode of operation only. The barcode scanners currently in use project the pattern from a single aperture. In order for a user to use the device in portable mode, extensive orientation of the bar code scanner is required to aim the scan pattern at the bar code. Once the bar code has been read, further manipulation is required to return the scanner to a position suitable for fixed scanning.